[PATCH 21/26] ext4: Remove wait for unwritten extent conversion from ext4_truncate()

[Jan Kara <jack@suse.cz>]

Since PageWriteback bit is now cleared after extents are converted from
unwritten to written ones, we have full exclusion of writeback path from
truncate (truncate_inode_pages() waits for PageWriteback bits to get cleared
on all invalidated pages). Exclusion from DIO path is achieved by
inode_dio_wait() call in ext4_setattr(). So there's no need to wait for
extent convertion in ext4_truncate() anymore.

Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/inode.c   | 6 ------
 fs/ext4/page-io.c | 9 ++++++++-
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4273b4d..deab352 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3742,12 +3742,6 @@ void ext4_truncate(struct inode *inode)
 			return;
 	}
 
-	/*
-	 * finish any pending end_io work so we won't run the risk of
-	 * converting any truncated blocks to initialized later
-	 */
-	ext4_flush_unwritten_io(inode);
-
 	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
 		credits = ext4_writepage_trans_blocks(inode);
 	else
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 755741c..0f65561 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -158,7 +158,14 @@ static void ext4_clear_io_unwritten_flag(ext4_io_end_t *io_end)
 		wake_up_all(ext4_ioend_wq(inode));
 }
 
-/* check a range of space and convert unwritten extents to written. */
+/*
+ * Check a range of space and convert unwritten extents to written. Note that
+ * we are protected from truncate touching same part of extent tree by the
+ * fact that truncate code waits for all DIO to finish (thus exclusion from
+ * direct IO is achieved) and also waits for PageWriteback bits. Thus we
+ * cannot get to ext4_ext_truncate() before all IOs overlapping that range are
+ * completed (happens from ext4_free_ioend()).
+ */
 static int ext4_end_io(ext4_io_end_t *io)
 {
 	struct inode *inode = io->inode;
-- 
1.8.1.4